Small Iowa city evacuated due to chemical fire

In this image from video provided by KIMT-TV is smoke rises from a fire in Northwood, Iowa, Thursday, Feb. 20, 2014. Authorities say an evacuation order is in place for Northwood due to a fire at a fertilizer plant at Northwood Municipal Airport. No one is reported injured. (AP Photo/KIMT-TV, Levi Ismail)

NORTHWOOD, Iowa (AP) — Authorities are evacuating residents of a small northern Iowa city where firefighters are battling a chemical fire.

The Worth County Sheriff's Office says an evacuation order is in place for Northwood due to a fire Thursday morning at a fertilizer plant at Northwood Municipal Airport.

Mercy Medical Center-North Iowa in nearby Mason City says four people have sought treatment at the hospital. Their conditions have not been released.

A National Weather Service alert says the fire contains sulfuric acid.

The Mason City Globe Gazette reports several residents heard explosions when the fire broke out. Highway 105, a main artery in Northwood, was blocked off near the fire.

The Iowa State Patrol, Northwood police and the sheriff's department are assisting at the scene.